1. Field of the Invention
The present invention relates to a two-cylinder overhead-valve V-engine and, more specifically, to improvements in the arrangement of an air intake passage and a cooling water passage in a water-cooled two-cylinder overhead-valve V-engine.
2. Description of the Related Art
FIG. 11 shows a conventional water-cooled two-cylinder overhead-valve V-engine in which a head cover and a carburetor are removed. An intake valve rocker arm 102 and an exhaust valve rocker arm 103 are placed on the cylinder head 101 of each cylinder. The intake valve rocker arm 102 has one end in contact with an intake valve and the other end in contact with an intake valve driving push rod 106. The exhaust valve rocker arm 103 has one end in contact with an exhaust valve 107 and the other end in contact with an exhaust valve driving push rod 108.
The cylinder head 101 is provided with an air intake port 110 in one end part thereof on one side with respect to a direction parallel to the axis O1 of a crankshaft, and an exhaust port 111 in the other end part thereof on the other side with respect to the direction parallel to the axis O1 of the crankshaft. A water jacket has an outlet 113 formed in a part of the cylinder head 101 on the side of the air intake port 110.
An intake manifold 120 is disposed on the side of the air intake port 110 and has an air intake passage 131 and a cooling water passage 121 adjacent to the air intake passage 131. The air intake passage 131 has one end directly connected to the air intake port 110 of the cylinder head 101 of one of the two cylinders, and the other end connected through a thermostat case 115 to the air intake port 110 of the cylinder head 101 of the other cylinder. The cooling water passage 121 has one end directly connected to the outlet 113 of the water jacket of one of the two cylinders, and the other end connected through the thermostat case 115 to the outlet 113 of the water jacket of the other cylinder.
The thermostat case 115 includes a first cooling water inlet 116 connected to the outlet of the water jacket, a second cooling water inlet 122 connected to the cooling water passage 121 of the intake manifold 120, a first cooling water outlet 125 connected to a water pump by a bypass pipe 124, a second cooling water outlet 118 connected to a cooling water return opening of a radiator, and a thermostat 114. The thermostat 114 measures the temperature of cooling water at the outlet of the water jacket, connects the cooling water passage 121 to the bypass pipe 124 when the measured temperature is lower than a set temperature or to the radiator when the measured temperature is not lower than the set temperature.
The intake manifold 120 is provided in its upper middle part with an inlet opening 137. The inlet opening 137 is connected to a carburetor, not shown, disposed above the intake manifold 120.
FIG. 12 is an enlarged sectional view taken on line XIIxe2x80x94XII in FIG. 11. Push rods 106 and 108 are extended in substantially parallel to each other into the cylinder head 101 and a cylinder block 140. The lower ends of the push rods 106 and 108 respectively rest on tappets 141 engaging a camshaft 142.
As shown in FIG. 11, when the air intake port 110 and the cooling water outlets 113 are formed in the end parts of the cylinder head on one side with respect to the direction parallel to the axis O1 of the crankshaft, and the air intake ports 110 and the cooling water outlets 113 are connected by the intake manifold 120 disposed on the side of the air intake ports 110, the engine inevitably has a big dimension along the direction of the axis O1 of the crankshaft, and the air intake passage between the carburetor and the air intake port 110 of each cylinder head 101 is inevitably long. An art relating with the present invention is disclosed in Japanese Laid-Open Publication No. Hei 10-159510.
Accordingly, it is an object of the present invention to provide a water-cooled two-cylinder overhead-valve V-engine of compact construction having short air intake passages by changing opening positions of air intake ports and cooling water outlets of water jackets so as to use a bank space effectively.
The present invention a two-cylinder overhead-valve V-engine includes: a pair of cylinders arranged so as to form a V-shape in which a V-bank is formed, each of said cylinders including a cylinder head with an intake valve and an exhaust valve; a camshaft disposed below said V-bank in parallel to an axis of a crankshaft; intake valve rocker arms for operating said intake valves, respectively; exhaust valve rocker arms for operating said exhaust valves, respectively; and push rods for operating said intake valve rocker arms and said exhaust valve rocker arms, respectively, said push rods being connected to said camshaft by tappets, respectively, each pair of said push rods for each of said cylinders being extending gradually away from each other toward each of valve rocker arm chambers in which said valve rocker arms are housed, wherein, between each pair of said push rods for each of said cylinders, each of air intake passages with air intake ports for said cylinder heads is formed, each of said air intake ports being formed so as to open into said V-bank, each of said air intake ports being connected by each of said air intake passages formed in said V-bank to a carburetor disposed in said V-bank.
Since the V-bank can be used effectively for installing the intake manifold and the carburetor, this two-cylinder overhead-valve V-engine has a comparatively small dimension in the direction of an axis of a crank shaft, and the carburetor can be connected to the air intake ports of the cylinder heads by short, straight air intake passages. Consequently, the passage resistance of the air intake passages is small. The engine is able to respond quickly to throttle opening adjustment. Moreover, the stagnation of the fuel and the oil in the air intake passages can be prevented.
Preferably, together with said air intake ports, cooling water outlets of water jackets for said cylinders are formed so as to each open between each pair of said push rods for each of said cylinders, said cooling water outlets of said water jackets being connected by a cooling water passage adjacent to said air intake passages disposed in said V-bank.
Accordingly, part of the cooling water pipe system can be disposed in the V-bank so as to be simplified with the result that the two-cylinder overhead-valve V-engine can be formed in compact construction. Since the cooling water passage through which the cooling water heated in the water jacket flows is formed adjacently to the intake air passages, walls forming the intake air passages are heated to promote the gasification of the fuel flowing through the air intake passages.
Preferably, said cooling water passage connecting said cooling water outlets of said water jackets is provided with a cooling water outlet connected to a radiator.
Accordingly, the cooling water pipe system can be formed in a simple, compact arrangement and the engine can be formed in compact construction.